Although it has long been recognized that human antibodies are superior to mouse antibodies for therapeutic use, the reverse has been thought to be the case for in vitro diagnostics. The different perceived roles of human and mouse antibodies reflect differences in their properties and methods of preparation. The principal hitherto recognized advantages of human antibodies relative to mouse antibodies are lack of human anti-mouse (HAMA) response on administration to a patient, longer in vivo half-life, and better interaction with human complement. All of these advantages account for the superiority of human antibodies to mouse antibodies for therapeutic use, but none is relevant to use of antibodies as reagents for in vitro diagnostics.
One of the principal advantages of mouse antibodies relative to human antibodies is ease of isolation. Despite improvements in methods for producing human antibodies in recent years, it has still generally been considered to have been a simpler matter to produce a mouse antibody than a human antibody, particularly when the desired antibody is sparsely represented in the total repertoire of antibodies that must be screened. Another advantage of mouse antibodies is that the mouse antibody constant region can be detected using a labelled anti-mouse antibody, typically prepared from another species, such as a goat, as a detection moiety. Such an antibody binds specifically to a mouse antibodies without binding to human antibodies present in the sample. Use of a secondary labelling moiety provides a useful format for detecting analytes in a human tissue sample. A comparable format cannot be used for human antibodies because an antibody against a human constant region would generate false positives by reacting with human antibodies in the sample. Because of their simplicity of isolation and compatibility with detection using a secondary labelling moiety, and because properties such as generation of a HAMA response, in vivo half life and complement activation are irrelevant for in vitro diagnostic purposes, mouse antibodies have been used for in vitro diagnostics to the virtual or total exclusion of human antibodies.
Although mouse antibodies are now in widespread use as diagnostic reagents, some problems have arisen when such antibodies are used to detect an analyte in a human sample. In some human samples, false positive or negative results are obtained due to the presence of HAMA or heterophilic antibodies in the sample. HAMA antibodies may be present in a human sample due to prior treatment of the patient from whom the sample was obtained with a mouse antibody (unrelated to the mouse antibody being used in diagnosis) or by environmental exposure to mouse antigens. Heterophilic antibodies are present in some patients as a response to certain pathogenic infections, such as Epstein Barr vinis. Either HAMA or heterophilic antibodies in a sample can bind to a mouse antibody being used as a diagnostic reagent thereby generating a false positive signal. In sandwich assay formats, HAMA or heterophilic antibodies can form a bridge between immobilized and solution antibodies to generate a false positive, as in other formats. Alternatively, in a sandwich assay format, some HAMA or heterophilic antibodies may bind to the immobilized antibody without binding to the solution antibody (or vice versa) thereby preventing immobilized antibody and solution antibody from bridging to each other through an analyte and thus generating a false negative. In consequence, a significant number of assays performed on human clinical samples using mouse antibodies as the diagnostic reagent generate inaccurate results.
U.S. Pat. No. 6,794,132, filed Dec. 1, 1999, WO98/47343, filed, Apr. 3, 1998, U.S. Pat. No. 6,555,310, filed Apr. 4, 1997 and U.S. Pat. No. 6,057,098, filed Apr. 4, 1997 are directed to related subject matter, and each is incorporated by reference in its entirety for all purposes.